1. Field of the Invention
The present invention relates to sol-gel compositions, and in particular, relates to hybrid sol-gel compositions having improved properties. In one embodiment, a coating may be formed of the composition to provide a surface having improved properties such as increased hardness, abrasion resistance, impact resistance, and chemical resistance.
2. Description of the Related Art
Sol-gel reactions to form siloxane matrices are known. The sol-gel reaction occurs in two distinct steps, as shown below.

In the first step (1), an alkoxysilane is hydrolyzed by water to form the corresponding silanol. This step can be acid or base catalyzed, although acid catalyzed systems are typical for commercial systems.
In the second step (2a), a condensation reaction between two silanol molecules forms a siloxane (Si—O—Si) bond. Depending on the molecular structure of the alkoxysilane, after hydrolysis, the condensation step can then repeat in two or more directions forming a matrix. The gelation or matrix formation is the film-forming step.
The entire reaction sequence can take place at room temperature or at elevated temperatures. Curing or condensation of the formed silanols is much slower than the hydrolysis. Curing can occur very slowly at room temperature, but commercially curing is typically accomplished in a box or tunnel oven.
Typical siloxane coatings based on sol-gel reactions form highly crosslinked matrices which tend to be very brittle and easily chipped. The excessive brittleness leads to very low scratch and abrasion resistance.
Typical hybrid compositions including a siloxane matrix and organic polymers generally are admixtures of an already-formed inorganic matrix and an organic polymer, or contain organic polymers having alkoxysilane groups that can undergo sol-gel condensation reactions. These compositions involve complex synthesis and tend not to be commercially viable. Additionally, the typical hybrid compositions have a low use temperature due to the organic polymers used, thereby limiting their applications.
Improvements in the foregoing are desired.